Engine control unit and a vehicle equipped with it

Abstract

Engine control unit with a drive circuit (14) that drives a motor (M1) that generates a torque to obtain a driving force of a vehicle (100), and a control section (30) which controls the drive circuit (14), wherein the control section (30) controls the drive circuit (14) using a limiting value such that the motor (M1) performs a limited operation, the limiting value being determined according to a switching frequency of a switching device (Q3, Q4, Q5, Q6, Q7, Q8) included in the drive circuit and a temperature of the switching device, and the control section (30) controls the drive circuit (14) by selecting the switching frequency according to a speed of the motor and a torque requested by the motor (M1), wherein the limit value is determined based on a torque limit value, and the torque limit value is determined in advance according to the switching frequency and the temperature of the switching device (Q3, Q4, Q5, Q6, Q7, Q8).

Description

Background of the invention 1. Field of the invention

[0001] The invention relates to an engine control unit and a vehicle equipped with this engine control unit. 2. Description of the state of the art

[0002] Motor drive control systems in which a motor is driven by an inverter are used in various fields. In such systems, an inverter circuit for driving a motor includes switching devices such as an IGBT device, a power MOS device, and the like. Since these switching devices can be damaged by high temperatures, the torque is usually limited when the temperature of the inverter rises.

[0003] Japanese Patent Application No. JP H09 - 121 595 A describes a thermal protection device for a power converter capable of thermally protecting a switching device of an inverter circuit without reducing torque even if the temperature of the switching device becomes high.

[0004] When a detected temperature of the switching device rises, the thermal protection device executes a control that first switches from a high carrier frequency to a low carrier frequency without torque limitation. Then, if the temperature continues to rise, the device sets a torque limit value to a small value.

[0005] Further prior art is described in Japanese Patent Application No. JP H07-322 401 A.

[0006] Recently, environmentally friendly vehicles such as electric vehicles, hybrid vehicles, fuel cell vehicles, and the like have been receiving considerable attention. These types of vehicles are equipped with a motor driven by a DC power source and an inverter. The motor generates drive torque for the vehicle.

[0007] However, due to the demand to reduce the cost and installation space of the inverter that drives the motor, there is a trend toward smaller inverters with lower heat capacity. If such an inverter is used, a sharp rise in temperature is likely to occur due to heat concentration. This temperature rise is particularly noticeable at higher carrier frequencies, at which switching is frequently performed.

[0008] It should be noted that a carrier frequency fc, which determines the switching frequency, is set based on the speed of the motor and the requested torque.

[0009] Fig. 5A and Fig. 5B show conceptual diagrams illustrating the carrier frequency.

[0010] Fig. Figure 5A shows a case where the carrier frequency fc is 1.25 kHz. This carrier frequency is used as a basis for PWM control of on / off waveforms, causing a current ICOIL to flow.

[0011] In contrast, Fig. 5B shows a case where the frequency of the current ICOIL is higher than that according to Fig. 5A. In this case, the carrier frequency fc must be increased to 2.5 kHz to ensure a uniform flow of current ICOIL. PWM control is performed at this carrier frequency to turn the switching device on and off. By reducing the carrier frequency instead of limiting the torque, the number of switching operations can be reduced. Thus, the switching loss can be reduced, which can suppress the temperature rise by an amount corresponding to the reduction in switching loss. However, this does not necessarily allow the motor to rotate smoothly, and thus, motor vibration may increase.

[0012] Fig. Figure 6 illustrates the carrier frequency and temperature rise of the switching device.

[0013] Fig. 6 shows a case where the initial temperature is 65°C. In this case, when the carrier frequency fc is 1.25 kHz or fc is 2.5 kHz, the temperature of the switching device does not rise to 110°C, which is the temperature at which the switching device is damaged, even if the motor operating time is extended.

[0014] In contrast, when the carrier frequency fc is 5 kHz, the switching loss increases by the amount by which the switching frequency is higher, and the switching loss generates heat. Therefore, if the initial temperature is 65°C, as in the case where the carrier frequency fc is 1.25 kHz or 2.5 kHz, the temperature may exceed 110°C after a time t1. Accordingly, if the carrier frequency is high, the device will be damaged unless countermeasures are taken. Summary of the invention

[0015] The present invention has for its object to provide an engine control unit and a vehicle equipped with the unit, which can generate a preliminary torque to the maximum possible extent and at the same time can suppress a temperature rise of the switching device.

[0016] This object is achieved by an engine control unit as defined in claim 1 and alternatively by a vehicle as defined in claim 3.

[0017] An advantageous embodiment is specified in patent claim 2.

[0018] According to the embodiment of the invention, in the engine control unit and the vehicle equipped with the unit, the required torque can be generated to the maximum possible extent and at the same time a switching device can be protected. Short description of the drawings

[0019] The above and / or other objects, features, and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the accompanying drawings, in which like or corresponding portions are designated by the same reference numerals. In the drawings: Fig. 1 is a circuit diagram illustrating a structure of a vehicle 100 equipped with an engine control unit according to the invention, Fig. 2 is a flowchart showing a control routine for a control unit 30 according to Fig. 1 illustrates, Fig. 3 is a diagram illustrating a carrier frequency fc, Fig. 4 is a diagram illustrating torque limiting maps obtained in steps S4, S6 and S8 according to Fig. 2 can be used, Fig. 5A and Fig. 5B Conceptual diagrams illustrating the carrier frequencies, and Fig. 6 is a diagram illustrating the carrier frequency and the temperature rise. Detailed description of the preferred embodiment

[0020] An embodiment of the invention will be described in detail below with reference to the drawings. Note that the same or corresponding portions are designated by the same reference numerals, and a repeated description thereof is omitted.

[0021] Fig. 1 shows a circuit diagram of a structure of a vehicle 100 equipped with an engine control unit according to the invention.

[0022] The vehicle 100 is equipped with a battery B, a voltage sensor 10, system main relays SR1, SR2, a capacitor C1, a voltage converter 20, an inverter 14, a temperature sensor 35, a current sensor 24 and a control unit 30.

[0023] Battery B is a secondary battery such as a nickel-metal hydride battery, a lithium-ion battery, or the like. The voltage sensor 10 detects a DC voltage VB output from battery B and outputs a signal representing the detected DC voltage to the control unit 30. The system main relays SR1 and SR2 are turned on or off by a signal SE from the control unit. More specifically, the system main relays SR1 and SR2 are turned on when the signal SE is at a high level (high logic level) and are turned off when the signal SE is at a low level (low logic level). The capacitor C1 smooths the voltage between the terminals of battery B when the system main relays SR1 and SR2 are turned on.

[0024] The voltage converter 20 has a voltage sensor 21, a current sensor 11, a boost converter 12, a capacitor C2 and a voltage sensor 13.

[0025] The current sensor 11 detects a direct current flowing between the battery B and the boost converter 12. The current sensor 11 then outputs a direct current signal IB (IB signal) representing the detected current to the control unit 30.

[0026] The boost converter 12 includes a reactance L1, IGBT devices Q1 and Q2, and diodes D1 and D2. The reactance L1 is connected at one end to a positive electrode of battery B via the system main relay SR1. The IGBT devices Q1 and Q2 are connected in series between the output terminals of the boost converter 12, which outputs a voltage VH. The diodes D1 and D2 are connected in parallel to the IGBT devices Q1 and Q2, respectively.

[0027] The other end of the reactance L1 is connected to an emitter of the IGBT device Q1 and to a collector of the IGBT device Q2. A cathode of the diode D1 is connected to a collector of the IGBT device Q1, while an anode of the diode D1 is connected to the emitter of the IGBT device Q1. A cathode of the diode D2 is connected to the collector of the IGBT device Q2, while an anode of the diode D2 is connected to an emitter of the IGBT device Q2.

[0028] The voltage sensor 21 detects a voltage on the input side of the boost converter 12, namely a voltage VL. The current sensor 11 detects a current flowing to the reactance L1, namely a current IB. The capacitor C2 is connected to the output side of the boost converter 12 and stores energy supplied from the boost converter 12. The capacitor C2 also smooths the voltage. The voltage sensor 13 detects a voltage on the output side of the boost converter 12, that is, the voltage between the electrodes of the capacitor C2, namely a voltage VH.

[0029] The inverter 14 drives an AC motor M1 with a boosted voltage supplied from the boost converter 12. The inverter 14 also feeds electrical power generated by the AC motor M1 in connection with regenerative braking back to the boost converter 12. The boost converter 12 is controlled by the control unit 30 to operate as a buck circuit.

[0030] The AC motor M1 is a motor for generating torque to drive a driven wheel (not shown) of the vehicle 100. This motor may be suitable, for example, for a hybrid vehicle. Specifically, the motor may operate as a generator driven by an internal combustion engine (not shown) and may also operate as an electric motor for the internal combustion engine, which may start the internal combustion engine.

[0031] The converter 14 has a U-phase branch 15, a V-phase branch 16, and a W-phase branch 17. The U-phase branch 15, the V-phase branch 16, and the W-phase branch 17 are connected in parallel between output lines of the boost converter 12.

[0032] The U-phase arm 15 includes IGBT devices Q3 and Q4 and diodes D3 and D4. The IGBT devices Q3 and Q4 are connected in series with each other, and the diodes D3 and D4 are connected in parallel with the IGBT devices Q3 and Q4, respectively. A cathode of the diode D3 is connected to a collector of the IGBT device Q3, whereas an anode of the diode D3 is connected to an emitter of the IGBT device Q3. A cathode of the diode D4 is connected to a collector of the IGBT device Q4, whereas an anode of the diode D4 is connected to an emitter of the IGBT device Q4.

[0033] The V-phase branch 16 includes IGBT devices Q5 and Q6 and diodes D5 and D6. The IGBT devices Q5 and Q6 are connected in series with each other, and the diodes D5 and D6 are connected in parallel with the IGBT devices Q5 and Q6, respectively. A cathode of the diode D5 is connected to a collector of the IGBT device Q5, whereas an anode of the diode D5 is connected to an emitter of the IGBT device Q5. A cathode of the diode D6 is connected to a collector of the IGBT device Q6, whereas an anode of the diode D6 is connected to an emitter of the IGBT device Q6.

[0034] The W-phase branch 17 includes IGBT devices Q6 and Q8 and diodes D7 and D8. The IGBT devices Q7 and Q8 are connected in series with each other, and the diodes D7 and D8 are connected in parallel with the IGBT devices Q7 and Q8, respectively. A cathode of the diode D7 is connected to a collector of the IGBT device Q7, whereas an anode of the diode D7 is connected to an emitter of the IGBT device Q7. A cathode of the diode D8 is connected to a collector of the IGBT device Q8, whereas an anode of the diode D8 is connected to an emitter of the IGBT device Q8.

[0035] An intermediate point of each phase branch 15, 16, and 17 is connected to respective ends of U-phase, V-phase, and W-phase coils of the AC motor M1. The AC motor M1 is a three-phase permanent magnet motor, with one end of each of the three coils connected to the others at a midpoint between them. The other end of the U-phase coil is connected to a connection node of the IGBT devices Q3 and Q4. The other end of the V-phase coil is connected to a connection node of the IGBT devices Q5 and Q6. The other end of the W-phase coil is connected to a connection node of the IGBT devices Q7 and Q8.

[0036] The current sensor 24 detects a current flowing through the AC motor M1, namely a motor current MCRT1. The current sensor 24 then outputs the motor current MCRT1 to the control unit 30.

[0037] The temperature sensor 35 detects a temperature of the inverter 14 and outputs an inverter temperature signal (inverter temperature signal T). Note that the inverter temperature T corresponds to the temperature of the switching devices Q3 to Q8.

[0038] The motor control unit 30 receives signals for a torque command value TR1, a speed of the motor MRN1, the voltages VB, VL, and VH, the current IB, the motor current MCRT1, and the inverter temperature T. The control unit 30 outputs a boost instruction PWU and a step-down instruction PWD to the voltage converter 20. Furthermore, the control unit 30 outputs a drive instruction PWMI1 and a regeneration instruction PWMC1 to the inverter 14. The drive instruction PWMI1 instructs the inverter 14 to convert the DC voltage output from the boost converter 12 into an AC voltage to drive the motor M1. The regeneration instruction PWMC1 instructs the inverter 14 to convert the AC voltage generated by the motor M1 into a DC voltage to output the DC voltage to the boost converter 12 side.

[0039] The operation of the voltage converter 20 is briefly described below. The boost converter 12 in the voltage converter 20 functions as a boost circuit, which acts as a forward conversion circuit that supplies the electrical power from the battery B to the inverter 14 in a motor mode. In contrast, in a regeneration mode, the boost converter 12 functions as a buck circuit, which serves as a reverse conversion circuit that charges the electrical power generated by the motor M1 to the battery B.

[0040] The boost converter 12 operates as a boost circuit in which the IGBT device Q2 is turned on and off when the IGBT device Q1 is off. Specifically, when the IGBT device Q2 is turned on, current flows along a path from the positive electrode of the battery B to the negative electrode of the battery B via the reactance L1 and the IGBT device Q2. As the current flows, energy is stored in the reactance L1.

[0041] When the IGBT device Q2 is turned off, the energy stored in the reactance flows to the inverter 14 side via the diode D1. As a result, the voltage between the electrodes of the capacitor C2 increases. Accordingly, the output voltage of the boost converter 12, which is applied to the inverter 14, is amplified.

[0042] In contrast, the boost converter 12 operates as a buck circuit in which the IGBT device Q1 is turned on and off when the IGBT device Q2 is off. Specifically, when the IGBT device Q1 is turned on, the recovered current fed back via the inverter 14 flows through the IGBT device Q1 and the reactor L1 to the battery B.

[0043] Furthermore, when the IGBT device Q1 is turned off, a circuit including the reactance L1, the battery B, and the diode D2 is formed, and the energy stored in the reactance L1 is charged to the battery B. In this reverse conversion, the time period during which the inverter 14 supplies the electric power is longer than the time during which the battery B receives the electric power. Therefore, the voltage of the inverter 14 is extended and charged to the battery B. The operation of the voltage converter 20 is appropriately controlled by switching between the motor operation and the generator operation.

[0044] It should be noted that regenerative control involves the regeneration of power in a hybrid vehicle or an electric vehicle when the driver brakes the vehicle by applying a foot pedal. Regenerative control also involves the regeneration of power when the vehicle decelerates or when acceleration slows down when an accelerator pedal is released, even if the foot brake is not applied.

[0045] The control unit 30 controls the inverter 14 by selecting a switching frequency, namely a carrier frequency fc, according to the speed of the motor and the torque required by the motor M1.

[0046] The inverter 14 drives the motor M1 to generate torque for obtaining driving power of the vehicle. The control unit 30 controls the inverter 14 such that the motor M1 performs a restricted operation. The restricted operation is determined according to the carrier frequency fc of the IGBT devices Q3 to Q8, which serve as switching devices and are included in the inverter 14, and the inverter temperature T, which corresponds to the temperature of the switching devices.

[0047] If the inverter temperature becomes high, the control unit 30 limits the torque of the motor M1 so that the temperature of the inverter 14 cannot rise further. The torque limit is determined based on the inverter temperature T and the carrier frequency fc.

[0048] Fig. 2 shows a flowchart showing a control routine of the control unit 30 according to Fig. 1 illustrates.

[0049] First, in step S1, the control unit 30 reads the inverter temperature T detected by the temperature sensor 35.

[0050] Then, the control unit 30 reads the current carrier frequency fc in step S2.

[0051] The carrier frequency fc is related to the Fig. 3 described.

[0052] In Fig. 3, the horizontal axis indicates the speed N of the motor M1, and the vertical axis indicates the required torque of the motor M1. In the range where the speed N is equal to or within a boundary line W1, that is, in the range including point A, the carrier frequency fc is set to 1.25 kHz.

[0053] In the area between the boundary lines W1 and W2, i.e., in the area including point W, the carrier frequency fc is set to 2.5 kHz. In the area between the boundary lines W2 and W3, i.e., in the area including point C, the carrier frequency is set to 5 kHz.

[0054] The control unit 30 determines the carrier frequency based on the Fig. 3. In step S2 according to Fig. 2, the control unit uses the carrier frequency fc, which the control unit 30 itself determines.

[0055] In step S3, it is determined whether the carrier frequency fc is 1.25 kHz or not. If the carrier frequency fc is 1.25 kHz, processing proceeds to step S4. If not, processing proceeds to step S5.

[0056] In step S4, the control unit 30 reads a torque limit map for the carrier frequency of 1.25 kHz. Then, processing proceeds to step S9.

[0057] In step S5, it is determined whether the carrier frequency is 2.5 kHz. If the carrier frequency fc is 2.5 kHz, processing proceeds to step S6. If not, processing proceeds to step S7.

[0058] In step S6, the control unit 30 reads a torque limit map for the carrier frequency fc of 2.5 kHz. After completing step S6, processing proceeds to step S9.

[0059] In step S7, it is determined whether the carrier frequency fc is 5 kHz. If the carrier frequency fc is 5 kHz, the processing proceeds to step S8, where the control unit 30 reads a torque limit map for the carrier frequency fc of 5 kHz.

[0060] Note that even if the carrier frequency fc is not 5 kHz, processing still proceeds to step S8. Processing is performed in this manner because the torque limit map for the carrier frequency 5 kHz is the most stringent. The routine may be modified so that processing proceeds directly to step S8 without implementing the determination in step S7.

[0061] In step S8, the control unit 30 reads the torque limit map for the carrier frequency fc of 5 kHz. Then, the processing proceeds to step S9. In step S9, the control unit 30 controls the inverter 14 to rotate the motor with the torque limited by the determined torque limit value.

[0062] Then, the processing proceeds from step S9 to step S10, where the processing ends.

[0063] Fig. 4 illustrates the steps S4, S6 and S8 of Fig. 2 torque limiting maps used.

[0064] In Fig. 4, the horizontal axis indicates the inverter temperature T measured by the temperature sensor 35 according to Fig. 1 is detected. The vertical axis indicates the torque limit value, which is the condition that controls the drive of motor M1.

[0065] As it is in Fig. 4, the torque limit value is determined in advance according to the carrier frequency fc and the inverter temperature T, which is equivalent to the temperature of the switching devices.

[0066] When the carrier frequency fc is 1.25 kHz, the torque is not limited during actual driving. A predetermined torque of 100% is selected as the torque limit value in each temperature range.

[0067] When the carrier frequency fc is 2.5 kHz, if the inverter temperature T is equal to or greater than T2, a greater torque limit is imposed as the temperature increases. This means that the torque limit value becomes smaller.

[0068] When the carrier frequency fc is 5 kHz, if the inverter temperature T is lower than T2 but not lower than T1, the torque limit value is set smaller as the temperature becomes higher.

[0069] As it is in Fig. 6, for example, when an initial temperature is 65°C and the carrier frequency fc is 1.25 kHz or 2.5 kHz, even if the motor operating time is prolonged, the temperature does not rise to 110°C, which is the temperature at which the switching device is damaged.

[0070] On the other hand, when the carrier frequency fc is 5 kHz, the switching loss increases as the switching frequency increases, and the switching loss generates heat. Therefore, if the initial temperature is 65°C as in the case where the carrier frequency fc is 1.25 kHz or 2.5 kHz, the temperature may exceed 110°C after time t1. To avoid this, when the inverter temperature T is 65°C, the torque limit value is set to a small value only when the carrier frequency is 5 kHz. However, when the inverter temperature T is 65°C and operation is performed at a low carrier frequency, the required torque is not limited to the torque limit value.

[0071] With the structure described above, the required torque can be generated to the maximum possible extent and at the same time the switching device can be protected.

[0072] It should be noted that the rise of the inverter temperature T can be further suppressed by changing an application method of the torque limit value as described below.

[0073] In an operating range in which the carrier frequency fc does not increase even though the motor speed increases by at least a predetermined amount, the motor performs a restriction operation (restricted operation) based on the torque limit value. The torque limit value is determined in advance according to a preset carrier frequency fc and the inverter temperature T corresponding to the temperature of the switching devices. The above-determined operating range is a range defined, for example, by the boundary lines W1 and W2A in Fig. 3. In this range, the torque limit value is set according to Fig. 4 is selected based on the current carrier frequency fc of 2.5 kHz, and the motor performs limited operation.

[0074] In an operating range in which the carrier frequency fc increases when the motor speed increases by at least the predetermined amount, the motor can perform a limited operation based on the torque limit value determined in advance according to the increased carrier frequency fc and the inverter temperature T corresponding to the temperature of the switching devices. This range is a range defined, for example, by the boundary lines W2A and W2 in Fig. 3. In this range, instead of the current carrier frequency fc of 2.5 kHz, the torque limit value according to Fig. 4 is selected based on the increased carrier frequency fc of 5 kHz, and the motor performs limited operation.

[0075] That is, in the operating range where the carrier frequency is likely to increase after a predetermined time, the limiting value corresponding to a predicted carrier frequency higher than the current carrier frequency is used. Further, the carrier frequency may be predicted based on monitoring an increase / decrease in the speed of the motor. If the carrier frequency is predicted to increase, the limited operation is performed before this change by using the limiting value corresponding to the predicted carrier frequency higher than the current carrier frequency. Further, hysteresis may be provided for the use of the limiting value. If the carrier frequency is predicted to decrease, the limiting value corresponding to the current carrier frequency is applied without change.

[0076] According to this embodiment, the carrier frequency is adjusted based on the engine speed. Instead, the carrier frequency may be adjusted based on the vehicle speed.

[0077] Although the invention has been described with reference to an exemplary embodiment, it should be understood that the invention is not limited to the exemplary embodiment or the exemplary constructions. Rather, the invention is intended to cover various modifications and equivalent arrangements. In addition, although the various elements of the exemplary embodiment are shown in various combinations and configurations, which are intended to be exemplary, other combinations and configurations, including more, fewer, or only a single element, are also within the scope of the invention.

Claims

[1] Engine control unit with a drive circuit (14) that drives a motor (M1) that generates a torque to obtain a driving force of a vehicle (100), and a control section (30) which controls the drive circuit (14), wherein the control section (30) controls the drive circuit (14) using a limiting value such that the motor (M1) performs a limited operation, the limiting value being determined according to a switching frequency of a switching device (Q3, Q4, Q5, Q6, Q7, Q8) included in the drive circuit and a temperature of the switching device, and the control section (30) controls the drive circuit (14) by selecting the switching frequency according to a speed of the motor and a torque requested by the motor (M1), wherein the limit value is determined based on a torque limit value, and the torque limit value is determined in advance according to the switching frequency and the temperature of the switching device (Q3, Q4, Q5, Q6, Q7, Q8). [2] Engine control unit according to claim 1, wherein the limiting value is determined on the basis of a torque limiting value determined in advance according to a current switching frequency and the temperature of the switching device (Q3, Q4, Q5, Q6, Q7, Q8) when the switching frequency does not increase even though a rotational speed of the motor (M1) increases by at least a predetermined amount, and, when the switching frequency increases when the speed of the motor (M1) increases by at least the predetermined amount, the limiting value is determined based on the torque limiting value determined in advance according to a predicted switching frequency higher than the current switching frequency and the temperature of the switching device (Q3, Q4, Q5, Q6, Q7, Q8). [3] Vehicle with a motor (M1) which generates a torque to obtain a driving force of the vehicle (100), and an engine control unit according to claim 1 or 2, which is arranged to control the engine (M1).

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